1. Field of the Invention
The present invention relates generally to a recess-type fastener for receiving a male fastener such as a screw and, more particularly, to such a recess-type fastener for fastening to thin plastic sheet material, for example a vacuum-formed plastic refrigerator inner liner.
2. Description of the Prior Art
In the field of fastening technology, it is frequently necessary to fasten to thin plastic sheet material. One example is in a household refrigerator where shelf supports or the like are attached to an inner liner formed of thermoplastic material. A mere screw-receiving aperture in the plastic is an unsatisfactory solution, except for extremely light loads, because insufficient area for thread engagement results and the entire load is concentrated on a very small portion of the plastic material. This can result in undesirable deformation or even cracking of the plastic sheet.
A typical prior art fastener for applying a heavy load to thin plastic sheet material comprises a separate plastic screw anchor applied to a suitable aperture in the plastic liner, generally from the rear side thereof. Such a separate plastic screw anchor typically includes a bore for receiving a screw and, additionally, a relatively large-diameter, force-distribution portion for contacting a significant area on the rear side of the plastic liner. This, of course, serves to distribute the load over a greater portion of the liner material. Such fasteners, while generally effective, represent an additional costly part required in the manufacture of a refrigerator.
An additional consideration in the design of a fastener for use in a refrigerator is compatibility with insitu foamed urethane thermal insulation material. During the foaming process, prior to solidification and hardening of the foam, large forces are developed which tend to force foam material through any apertures in the liner. Since typical prior art fasteners require an aperture in the inner liner, a sealing ring is typically employed, and this represents additional cost.